The document presents an overview of operating systems. It begins with an introduction that defines an operating system as software that controls computer resources and provides an interface for users. The document then discusses the structure of operating systems, including their role in managing resources and acting as an interface between hardware and users/programs. It outlines the main functions of operating systems such as process management, memory management, file management, security, and command interpretation. Finally, it briefly describes some popular operating systems like DOS, Unix, and Windows NT and concludes with the importance of operating systems for running applications and using computers.